Complete soot-free combustion of liquid fuel



Feb. 17, 1970 R. GYSI 3,495,576

' COMPLETE sooT-FhEE COMBUSTION 0F LIQUID FUEL Filed Sept. 11, 1967 3 Shee ts-Sheet 1 FIG.1 ye

JNVENTOR Rudolf Ggsi Feb. 17, 1970 R.-GY$I I 3, 5,

COMPLETE SCOT-FREE COMBUSTION OF LIQUID FUEL Filed Sept. 11. 196'! 5 Sheets-Sheet s .lNVENTOR Rudolf Ggsi United States Patent 3,495,576 COMPLETE SOOT-FREE COMBUSTION OF LIQUID FUEL Rudolf Gysi, 4853 Obermurgenthal, Switzerland Filed Sept. 11, 1967, Ser. No. 666,772 Claims priority, application Switzerland, Sept. 16, 1966, 13,422/ 66 Int. Cl. F22b 7/00; F231 /00; F2311 11/44 US. Cl. 122161 22 Claims ABSTRACT OF THE DISCLOSURE A system for complete soot-free combustion of liquid fuel, wherein the fuel is spread in a thin film on an evaporating surface and air is conducted over said film at high velocity, the evaporated fuel being combusted in a combusting chamber spaced from said evaporating surface.

This invention relates to a method and installation for soot-free combustion of liquid fuel, particularly heavy fuel oil. Liquid fuel is now usually combusted by means of oil burners in which the oil is atomized by fine nozzles in an air stream and combusted in the same. However, even with correct adjustment of the burner and suiticient air surplus complete combustion is never warranted, that is, minimum quantities of carbon monoxide and soot are always produced. It is well known that the chemical and physical contamination of the air by these products is considerable.

Evaporating oil burners are also known, in which the oil flows into a burner vessel and is directly combusted in the same. Under these circumstances complete combustion is never obtained and considerable quantities of soot and carbon monoxide are produced.

This invention aims in obtaining a complete combustion substantially by combination of features of the prior burner systems. The method according to this invention comprises in combination, providing an evaporating canal of flat cross section, admitting fuel to one wall of said evaporating canal thereby forming a thin film of fuel on said wall, setting up a forced flow of air passing over said film of fuel at high velocity, maintaining said wall at a temperature at least equal to the evaporating temperature of all constituents of said fuel and igniting the mixture of air and fuel at the exit of said evaporating canal. It has been found that under these conditions a complete combustion without production of soot and carbon monoxide is obtained. By clearly separating the evaporation from the combustion of the fuel and because the fuel is not injected into the air in more or less small particles, the fuel is combusted exclusively in gasified form, this being an important condition for complete and soot-free combustion. The separation of the evaporation and the combustion also allows sufficient intermixing of the fuel with the air for forming a practically homogeneous mixture resulting in a complete combustion.

Preferably, the burner is operated with an appreciable air surplus, for instance with at least double the stoichiometric air quantity. It was also found to be preferable to mix the fuel with air for forming a fuel foam or fuel emulsion with air, whereby rapid and complete evapora tion of all components of the fuel is assisted.

This invention also relates to an installation including a burner for complete soot-free combustion of liquid fuel, particularly heavy fuel oil. This installation comprises in combination an evaporating canal of flat cross section, a combustion chamber at the exit of said evaporating canal, a fan for setting up a forced air flow through said evaporating canal and combustion chamber, a heatable wall portion in said canal and a slit-shaped fuel nozzle opening onto said wall portion for admitting a film of fuel ICC thereon. The thin film of fuel formed on the wall portion of the evaporating canal is evaporated by the combustion air passing at high Velocity through the evaporating canal and the said wall portion is always maintained at a suflicient temperature for evaporating the fuel either by foreign electric heating when the burner is started or by radiation heating by the burner flame during operation of the burner.

The invention will now be explained in detail with reference to the drawings wherein an embodiment of the installation according to this invention is illustrated by way of example.

FIG. 1 shows the installation including a boiler with the burner in elevation and the boiler in vertical section,

FIG. 2 is a vertical section through the burner on a large scale,

FIG. 3 is a section along line III-IHin FIG. 2,

FIG. 4 is a section along line IVIV in FIG. 2, and

FIG. 5 is a section along line VV in FIG. 2.

The installation illustrated in the drawings comprises a burner 1 and a boiler 2. The burner casing is supported on a column 3 which is preferably displaceable in vertical direction and adapted to be locked in any desired vertical position, this allowing to remove the burner downwardly from the boiler 2 or to insert the burner upwardly into the illustrated operating position. The column 3 may form the piston or piston rod of a hydraulic lifting device.

The burner casing has a lower cylindrical casing portion 4 (FIG. 2) of sheet metal and an upper annular casing portion 5 of cast iron. An electric motor 6 is accommodated in the casing portion 4 for driving through a coupling 7, an excenter shaft 9 carrying an excenter disc 10 in a casing 8. As particularly shown in FIG. 5 the excenter disc 10 actuates four similar double-acting piston pumps 11 to 14. Two of these pumps serve for feeding fuel whereas the two other pumps serve for feeding air. All pump outlets tangentially enter into a central mixing chamber 15 of the casing 8 (FIG. 4), in which the admitted air is thoroughly whirled and intermixed with the admitted fuel for forming a foam or emulsion of fuel and air.

The mixing chamber 15 communicates with a vertical tube 16 having a number of radial exit openings 17 near its upper end. These exit openings communicate with a slit 18 formed between a filling body 19 fixed on the tube 16 and a circular, practically plane plate 20. The width of the slit 18 is exaggerated in the drawing and in fact this slit has a width of about .4 mm. at its opening.

The plate 20 is an electrical heating plate having heating coils (not illustrated) in the grooves at its lower side. Plate 20 also has a gutter 21 along its rim for collecting fuel that might not be evaporated on the plate 20. The gutter 21 rests on an inwardly directed flange of casing portion 5, a sealing ring 22 being inserted between the gutter and flange. The space below the plate 20 is closed by means of a cup 23 of sheet metal. This space serves for accommodation of the electrical conductors for the heating plate 20 and of a thermostat for control of the plate temperature. A dish-shaped cover 24 of cast iron rests on the plate 20 and on outwardly extending flanges of the casing portion 5, a sealing ring 22' being inserted between portions 5 and 25. The casing portion 5, the plate 20 and the cover 24 thus define a closed annular space which is relatively wide at its outer rim, decreases in width inwardly and is widened again from the edge 25 inwardly. Near this edge 25 (FIGS. 2 and 3) the cover 24 has an exit tube 26 into which the filling body 19 extend. Curved guide vanes 27 are provided at the lower side of cover 24, such guide vanes contacting the plate 20 and defining spiral-shaped flow canals tapering inwardly between the plate 20 and the cover 24.

A tube 29 is coaxially disposed above the exit tube 26 which enters into the lower end of tube 29 with radial clearance. The tube 29 is supported on a shoulder of cover 24 by means of a conical ring 30 of sheet metal. The ring 30 has cuttings 31 at its lower end. A double-wall ring 32 of sheet metal is disposed above the ring 30, surrounding with radial clearance the tube 29 and supported on the cover 24. The outer, downwardly formed flange 32' or ring 32 is the outer limitation of the burner. As shown in FIG. 1 this flange engages with some radial clearance into the lower opening of the boiler casing. Ignition electrodes 33 are disposed above the tube 29. The one electrode carrier 34 is insulated from the burner casing whereas the other electrode carrier 35 is fixed to the flanges of the casing portion and cover 24 respectively without insulation.

An air inlet pipe 36 connected to a fan not illustrated opens into the space formed between the plate 20 and the cover 24 for admitting combustion air into this space.

The cylindrical mantle 37 of the boiler illustrated in FIG. 1 is supported on rods 39 by means of laterally projecting brackets 38, the rods 39 being fixed in a wall of the heating room in a manner not shown in the drawing. The boiler has three similar cylindrical heat exchangers 40, 41 and 42 interconnected by means of tubes 43 in such a way that the heated medium alternatively flows in opposite direction through the heat exchangers. Heat exchangers 40 and 42 are connected with their lower extensions 44 to a lower wall 45 of the boiler mantle whereas the middle heat exchanger 41 is connected to the upper wall 46 of the boiler mantle. In this way series-connected relatively narrow flow canals 47, 48 and 49 are formed between the heat exchangers 40 to 42, through which the combustion gases flow alternatively in upward and downward direction during operation of the burner. The outer flow canal 49 is connected to the chimney. The boiler has a central frustoconical chamber 51 of which the lower end is connected to the innermost heat exchanger by means of curved tubes 52. The upper end of the chamber 51 communicates with the outlet pipe 53 of the boiler and the outermost heat exchanger 40 communicates with the return pipe 54 of the heating system. The space formed between the innermost heat exchanger 42 and the chamber 51 and tapering upwardly communicates with the innermost flow canal 47 above the innermost heat exchanger 42. The annular groove 55 formed by the extensions 44 and the mantle wall 45 serves as a gutter for water condensing in the canals 47 and 48, this water being drained through a pipe 56.

The installation described above may be manually started and controlled, but preferably it is controlled by automatic means as follows:

For starting the burner, the plate 20 is first electrically heated to a predetermined upper temperature limit at which the thermostat automatically cuts out the heating circuit. Upon reversal of the thermostat switch the motor 6 and the fan are manually or automatically started. Fuel and air are thus delivered to the mixing chamber by pumps 11 to 14 and mixed or emulgated in the same, and the so foamed or e'mulgated fuel flows through the tube 16, the apertures 17 of the same and the slit nozzle 18 onto the plate 20. The fuel which will already be heated in the tube 16 rapidly evaporates on the heated plate 20. The combustion air enters from the fan through the tube 36 into the space defined between plate 60 and cover 24 and then flows in the form of a whirl between the guide vanes 27 and over the plate inwardly and takes up the evaporated fuel with which it is intensively intermixed in the outlet pipe 26. The velocity of the combustion air and of the combustible mixture respectively gradually increases until it is again slowed down after its deflection into vertical direction in the pipe 26. The maximum veloc ity of the combustion air or mixture respectively exceeds the velocity of propagation of combustion in the mixture so that no combustion is possible in the inwardly tapering evaporating canal formed between plate 20 and cover 24 and consisting of a number of separate canals. The combustion is thus clearly separated from the evaporation. In fact combustion only starts in and above the tube 29 whereby the electrical ignition is started together with the fuel pump and the fan in order to ignite the mixture as soon as it reaches a concentration suflicient for combustion. The combustion gases flow through the boiler as explained above, and due to the complete sootfree combustion of the mixture it is possible to cool down the combustion gases until appreciable condensation occurs. Therefore, the high efliciency of the installation is not only due to the complete combustion but also to the possibility of high utilisation of the caloric capacity of the combustion gases. Under special circumstances it may even be possible to operate the installation without chimney, when all noxious components of the combustion gases, particularly sulfur dioxide, are absorbed in an absorbing unit.

When combustion has started, the cover 24 is heated by heat radiation and partially by heat conduction, whereby the plate 20 is indirectly heated to a temperature sufficient for continuous evaporation of the fuel. However, the electrical heating controlled by the thermostat remains operable for avoiding decrease of the temperature of plate 20 below a predetermined minimum temperature, for instance 250 C. When the combustion has properly started the ignition may be shut down, but a flame surveyor may be provided for operating the ignition in a well known manner when the flame should extinguish. During operation of the burner the sheets 30 and 32 are continuously cooled by the air circulation indicated in FIG. 2 by arrows.

The quantity of air delivered by the fan and the quantity of fuel delivered by the fuel pumps are so adjusted that approximately double the stoichiometric quantity of air is delivered. The maximum velocity of the air and the mixture respectively at the exit of the. evaporating canal exceeds the combustion velocity, that is, it is in the order of 20 to 30 m./sec. in order to avoid combustion in the evaporating canal. In fact the combustion takes place above the exit of pipe 26 in the tube 29 defining the combustion chamber of the burner. Good concentration of the mixture in the combustion zone by means of the pipe 26 and the tube 29 is particularly important because the mixture has an intensive rotation and would be expanded after leaving the pipe 26 whereby complete combustion would be injured. The form of the combustion chamber slightly tapering in its lower portion and widening in the upper portion as shown in FIG. 2 has been found by practical experience.

The following table shows values measured on the installation as shown in FIG. 1 by the Eidgentissische Materialpriifungsanstalt:

Test

Duration minutes 90 60 (1) Oil consumption, kg./h 1. 7 1. 5 (2) Temperatures:

Combustion air, 0 17 17 Gas outlet, C 67 59 Outlet heating water, C- 67 Heating water inlet, C 55 51 (3) Analysis of combustion gas:

00;, contents, vol. percent. 10. 3 6. 6

C 0 contents, v01. percent" O. 0 0. O (4) Soot coefficient, RZ 0 0 (5) Chimney draft:

Outlet tube, mm. H2O 0. 1 0. 1

Combustion space, mm. H2O i0 i0 Calculated values:

Heat input, kcalJh ca. 17,000 ca. 15,000

Specific load of heating surfaces, kc lm ca. 2, 000 ca. 1, .000

Combustion losses, percent ca. 3-5 ca. 4-6

Various modifications of the installation as described and illustrated and of its operation are possible within the scope of this invention. Instead of piston pumps trochoid pumps may be used for delivering the fuel and air. The evaporating canal must not necessarily be subdivided into separate canals, but a single canal of flat cross section may be provided with the slit nozzle for the fuel at its bottom wall. Thermostatic control of the evaporating plate 20 may be dispensed with when the circuit is so dimensioned that the plate 20 is continuously heated with a reduced electric power after starting the combustion. The illustrated burner must not necessarily be used with a boiler. Due to the complete soot-free combustion the burner may preferably be used in drying plants and the like wherein the goods to be dried are directly exposed to and heated in the combustion gases.

What I claim is:

1. A method for soot-free combustion of liquid fuel particularly heavy fuel oil, comprising in combination, providing an evaporating canal of first cross section, admitting fuel to one wall of said evaporating canal thereby forming a thin film of fuel on said Wall, setting up a forced flow of air passing over said film of fuel at high velocity, maintaining said wall at a temperature at least equal to the evaporating temperature of allconstituents of said fuel and igniting the mixture of air and fuel at the exit of said evaporating canal, the air velocity being increased in said evaporating canal and decreased at the exit of said evaporating canal.

2. A method according to claim 1, characterized in that a foam or suspension of fuel in air is formed before admitting the fuel into said evaporating canal.

3. A method according to claim 1, wherein an air flow at least equal to double the stoichiometric quantity is admitted.

4. A method according to claim 1, wherein the velocity of the mixture at the exit of the evaporating canal is maintained above the combustion velocity, for instance in the range of 20 to 30 m./sec.

5. An installation including a burner for soot-free combustion of liquid fuel, particularly heavy fuel oil, comprising in combination an evaporating canal of flat cross section, a combustion chamber at the exit of said evaporating canal, a fan for setting up a forced air flow through said evaporating canal and combustion chamber, a wall portion in said canal, electrical heating means for said wall portion and a slit-shaped fuel nozzle opening onto and extending along said wall portion for admitting a film of fuel thereon.

6. An installation according to claim 5, wherein said fuel nozzle has an exit direction parallel to said wall portion adjacent the fuel nozzle, said wall portion of the evaporating canal forming the one wall of the fuel nozzle.

7. An installation according to claim 5, wherein the said evaporation canal has the form of a nozzle of which the cross section decreases in the flow direction of the air.

8. An installation according to claim 7, wherein the evaporation canal is a flat space enclosed between two circular plates.

9. An installation according to claim 8, wherein the upper horizontally disposed plate has a central exit tube, and an annular slit nozzle for the fuel is formed on the lower plate.

10. An installation according to claim 9, wherein the exit tube increases in width in the flow direction of the mixture, that is from its junction with the upper plate and its outlet end.

11. An installation according to claim 9, comprising a cover for the annular nozzle extending into the exit tube and forming an aerodynamic filling body therein.

12. An installation according to claim 9, wherein the width of the evaporation canal decreases from its outer end towards its inner end.

13. An installation according to claim 9, wherein the evaporating canal is subdivided into a number of separate canals by guide vanes.

14. -An installation according to claim 8, comprising an air inlet space surrounding the plates and communicating with the fan.

15. An installation according to claim 5, comprising at least one fuel pump and at least one air pump of which the outlets are connected to a mixing chamber for forming a foam or suspension of fuel in air, the outlet of said mixing chamber being connected to said fuel nozzle.

16. An installation according to claim 9, wherein the said exit tube extends into a combustion tube with radial clearance.

17. An installation according to claim 16, having a burner casing, said combustion tube being supported in the burner casing by means of conical sheets enclosing cooling air canals between each other.

18. An installation according to claim 16, comprising ignition electrodes at the outlet end of the combustion tube.

19. An installation according to claim 5, including a boiler to be heated by the combustion gases, said boiler comprising a number of concentrically disposed, cylindrical heat exchanger mantles between which canals for the combustion gases are disposed in series.

20. An installation according to claim 19, comprising a condensation gutter below said canals.

21. An installation according to claim 19, comprising a central boiler chamber widening from its lower end towards its upper end and communicating with the innermost exchanger mantle through tubes.

22. An installation according to claim 19, wherein the fluid to be heated flows through the boiler from the outer towards the inner boiler portions.

References Cited UNITED STATES PATENTS 1,585,201 5/1926 Nissinen 431-166 X 1,613,781 1/1927 Baker 431-166 X 1,969,371 8/1934 Hawley 431-l66 2,117,356 5/1938 Perry 431---238 2,246,809 6/1941 Miller 431238 X 2,630,168 3/1953 Farrell 431-208 3,234,991 2/ 1966 Fischbach 431-208 X CHARLES J. MYHRE, Primary Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION atent No. 3,495,576 February 17, 1970 Rudolf Gysi It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 5, line 16, "first" should read flat Signed and sealed this 29th day of December 1970.

(SEAL) Attest:

Edward M. Fletcher, Ir.

WILLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents 

